(1) Field of the Invention
The present invention relates to an evaluating method for NOx eliminating catalyst provided in an exhaust gas system of internal combustion engines, an evaluating apparatus therefor, and an efficiency controlling method therefor. The above described NOx eliminating catalyst means essentially a catalyst for eliminating NOx components in exhaust gas for cleaning the exhaust gas in the exhaust gas system of the internal combustion engine.
(2) Description of the Prior Art
As for a method for estimating efficiency decrease and deterioration of NOx eliminating catalyst, a method has been proposed in JP-A-4-265414 (1992), for example, wherein, taking a travelling distance of an automobile as a parameter, efficiency of NOx eliminating catalyst in the automobile is deemed to be sufficiently deteriorated when the travelling distance exceeds a designated value.
Further, a method for increasing an amount of hydrocarbon (called as HC hereinafter) when the HC used for NOx eliminating catalyst is deemed to be insufficient has been proposed in JP-A-3-229914 (1991).
However, there has been a problem that the prior art described above are unable to evaluate the catalyst correctly because they use a travelling distance as a parameter for evaluating the catalyst indirectly.
Furthermore, regarding to the prior art controlling the amount of HC, there has been a problem that the prior art can not control the amount of HC correctly because it controls the amount of HC irrelevant to the evaluating result of the catalyst deterioration.
(1) Objects of the Invention
In order to solve the above described problems, the object of the present invention is to provide a preferable evaluating method for NOx eliminating catalyst, a preferable evaluating apparatus for NOx eliminating catalyst, and a preferable efficiency evaluating method for NOx eliminating catalyst.
(2) Methods for solving the Problems
One of features of the present invention is essentially in an evaluating method of NOx eliminating catalyst for eliminating NOx components in exhaust gas, which is characterized in evaluating the NOx eliminating catalyst by comparing physical parameters of specified exhaust gas components both at an upstream side and a downstream side of the NOx eliminating catalyst.
Other one of the features of the present invention is essentially in an evaluating apparatus for NOx eliminating catalyst comprising;
(a) a base body composed of ion conductive solid electrolyte,
(b) platinum electrodes provided at both sides of the base body putting the base body between,
(c) diffused resistors covering the both electrodes respectively,
(d) exhaust gas inlet paths for flowing exhaust gas at upstream side of the NOx eliminating catalyst to one of the diffused resistors and flowing exhaust gas at downstream side of the NOx eliminating catalyst to the another of the diffused resistors respectively,
(e) an output portion which supplies an electrical signals output generated between the both platinum electrodes to a postfixed evaluating means.
Furthermore, other one of the features of the present invention is essentially in an efficiency controlling method for NOx eliminating catalyst for eliminating NOx components in exhaust gas, which is characterized in including the steps of evaluating the NOx eliminating catalyst first and subsequently elevating a temperature of the NOx eliminating catalyst or increasing an amount of HC.
In the above evaluating apparatus, oxygen concentration in exhaust gas at downstream of the NOx eliminating catalyst increases by reducing effect of the NOx eliminating catalyst. Therefore, efficiency and a deterioration degree of the NOx eliminating catalyst can be estimated by comparing physical parameters of specified gas components at upstream side and that at downstream side of the NOx eliminating catalyst.